Substrate Inductor Layer for RF Noise Filtering in MEMS Packages

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

RF signals conducted into MEMS microphones through solder pads result in demodulated signals in the audio band, considered noise, and existing RF filters using capacitors are costly and reduce electrostatic discharge robustness and electrical current limits.

Innovation Solution

Incorporating an inductor layer in the substrate of a sensor package as a single layer trace, positioned between layers furthest from the MEMS microphone or sensor, to act as a filter and increase electrical impedance, potentially replacing resistors and minimizing RF current to prevent heating and mechanical distortion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If RF filters using capacitors are employed to filter RF signals, then RF noise is reduced, but electrostatic discharge robustness and electrical current limits are reduced

Engineering Contradiction:

ImproveRF noiseVSAvoidelectrostatic discharge robustness

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent changes the electrical parameter characteristics by replacing capacitor-based filtering with inductor-based filtering. The inductor layer is configured with specific trace patterns (spiral, meander, or rectangular) and positioned at defined distances from the MEMS microphone to achieve RF filtering while maintaining electrostatic discharge robustness and electrical current limits that are compromised by capacitor-based solutions.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent substitutes the electrical filtering mechanism by replacing capacitive filtering with inductive filtering. The inductor is implemented as a planar trace structure on the PCB substrate, eliminating the need for discrete capacitor components and their associated drawbacks regarding electrostatic discharge robustness and current limits.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Object-affected harmful factors

If resistors are used to filter RF signals, then RF noise is reduced, but cost increases and electrostatic discharge robustness decreases

Engineering Contradiction:

ImproveRF noiseVSAvoidcost

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The patent merges the filtering function directly into the PCB substrate structure by implementing the inductor as a planar trace pattern on the substrate itself. This integration eliminates the need for separate resistor components, reducing overall cost while maintaining RF filtering effectiveness. The inductor trace is designed as part of the substrate's layered structure, combining multiple functions into a single integrated component.

Inventive Principle:

Principle #5Merging (Combining)

3Object-affected harmful factors

If inductor is placed on a layer close to MEMS microphone, then RF filtering is effective, but heating and mechanical distortion occur due to high RF current

Engineering Contradiction:

ImproveRF filtering effectivenessVSAvoidheating

Core Design Contradiction:

Object-affected harmful factorsVSTemperature

Solution Approach 1:

The patent resolves the heating issue by utilizing the vertical dimension of the multi-layer PCB substrate. The inductor layer is positioned on a specific layer (e.g., fourth layer in a six-layer substrate) at a defined distance from the MEMS microphone, effectively distributing RF current across different spatial dimensions and reducing localized heating and mechanical distortion while maintaining filtering effectiveness.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 inductor layer effectively filters RF signals, reducing noise and thermo-acoustic issues, while maintaining electrostatic discharge robustness and electrical current limits, thus enhancing the performance of MEMS microphone or sensor packages.

Implementation Method 1

Inductors can be used to increase the electrical impedance of a microphone nodes at RF frequencies, effectively acting as filters or mismatch mechanisms

Methodology Applied

Scientific EffectElectrical Impedance: Electrical Resistance

Implementation Method 2

The inductor can be configured as a single layer trace on an inductor layer within the substrate

Methodology Applied

Scientific EffectElectromagnetic Induction: Electromagnetic Induction

Data Source

PatentUS11912564B2Sensor package including a substrate with an inductor layer

Publication Date: 2024.02.27 KNOWLES ELECTRONICS LLC

AI summary

A sensor package can include a substrate including a plurality of layers. The plurality of layers can include a first pair of layers and a second pair of layers different from the first pair of layers. The substrate can have a first side and a second side opposite the first side. The sensor package can include a transducer coupled to the second side of the substrate. The sensor package can include an inductor electrically coupled to the transducer. The inductor can be configured as a single layer trace on an inductor layer within the substrate and disposed between the first pair of layers within the substrate. The first pair of layers can be more distal from the second side of the substrate than the second pair of layers.