Microphone Can Thickness and Material for RF Noise Attenuation
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Solution Overview
Problem
Microphone assemblies with MEMS transducers are susceptible to radio frequency (RF) induced noise and thermal fluctuations, leading to audible artifacts due to inadequate noise attenuation, which existing solutions attempt to address with liners but complicate fabrication and increase costs.
Innovation Solution
A microphone assembly with a thicker metal can, ranging from 6 mil to 12 mil in thickness, made of materials like stainless steel, titanium alloy, or Inconel, which acts as a Faraday cage and provides thermal diffusivity within the range of 2e−6 to 5e−6 m2/s, eliminating the need for a synthetic liner and simplifying fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a can liner made from liquid crystal polymer or polytetrafluoroethylene is disposed on the inside surface of the can, then RF induced temperature increases and thermal fluctuations are attenuated, but device complexity and manufacturing complexity increase
Solution Approach 1:
The patent removes the can liner component entirely and replaces it with a can made from a single material (Invar or Inconel) that inherently provides both RF shielding and thermal management properties. This extraction of the liner eliminates the multi-layer structure and reduces device complexity while maintaining the desired attenuation of RF induced temperature increases.
Solution Approach 2:
The patent combines the functions of RF shielding and thermal management into a single can structure made from Invar or Inconel. Instead of having separate can and liner components, the can itself is designed with material properties that provide both electromagnetic interference shielding and thermal diffusion, thereby reducing device complexity while addressing RF induced temperature increases.
2Temperature
If a can liner is disposed on the inside surface of the can, then thermal diffusivity is reduced to diffuse heat from surface currents, but manufacturing complexity and costs increase
Solution Approach 1:
The patent extracts the liner component from the design and relies on the can material itself (Invar or Inconel) to provide the necessary thermal management. This eliminates the need for separate liner manufacturing, bonding, and assembly processes, thereby reducing manufacturing complexity while maintaining control over the temperature of the back volume through the can's inherent thermal diffusivity properties.
Solution Approach 2:
The patent changes the material parameter of the can from standard materials to Invar or Inconel, which have specific thermal diffusivity properties that enable effective heat diffusion from surface currents. This parameter change in material selection allows the can itself to perform the thermal management function previously requiring a liner, thereby simplifying manufacturing while controlling temperature.
3Reliability
If a can liner is used to attenuate RF signals, then noise performance is improved, but the number of components and fabrication steps increase
Solution Approach 1:
The patent removes the liner component and achieves noise performance improvement through the can material (Invar or Inconel) and its thickness. This extraction reduces the number of components while maintaining or improving noise attenuation, as the single-material can design eliminates interfaces and potential failure points associated with liner-can assemblies.
Solution Approach 2:
The patent merges the RF shielding function and structural function into a single can component made from Invar or Inconel. This consolidation eliminates the need for a separate liner component, reducing the number of components and fabrication steps while maintaining noise performance through the inherent electromagnetic shielding properties of the chosen materials.
4Object-affected harmful factors
If the can thickness is increased to improve RF noise attenuation, then noise performance is improved, but manufacturing complexity increases
Solution Approach 1:
The patent changes the material parameter of the can to Invar or Inconel, which have superior RF shielding properties per unit thickness compared to standard materials. This material parameter change allows for optimized thickness (6-12 mil) that achieves the desired RF noise attenuation while remaining manufacturable, avoiding the need for excessively thick walls that would complicate manufacturing.
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 achieves superior RF noise attenuation and maintains signal quality while reducing fabrication complexity and costs, allowing for increased production rates without altering the package dimensions.
Implementation Method 1
The cover is formed of a single continuous material having a thickness within a range between approximately 6 mil and 12 mil... The cover material has a thermal diffusivity in a range between 2e−6 and 5e−6 m2/s... acts as a Faraday cage
Implementation Method 2
The cover material has a thermal diffusivity in a range between 2e−6 and 5e−6 m2/s... provides thermal diffusivity within the range of 2e−6 to 5e−6 m2/s
Data Source
AI summary
A microphone assembly includes a substrate, an acoustic transducer, an integrated circuit, and a cover couples to the substrate to enclose a back volume of the microphone assembly in which the acoustic transducer and the integrated circuit are disposed. The acoustic transducer includes a back plate and a diaphragm oriented parallel to the back plate disposed over an aperture in the substrate to receive acoustic signals. The cover is a metallic material with a thickness and a corresponding thermal diffusivity to attenuate incoming radio-frequency signals. The attenuation of the radio-frequency signals prevents ambient noise detectable by the microphone assembly.