Acoustic Sensor Substrate Design for Bonding Agent Run-up Prevention
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Solution Overview
Problem
Conventional acoustic sensors face issues with bonding agent run-up, leading to sensitivity degradation, substrate deformation, and increased costs due to the use of expensive ceramic substrates, as well as brittleness and back chamber leakage, which affect the reliability and sensitivity of the sensors.
Innovation Solution
The acoustic sensing element is designed with a substrate that includes a back chamber formed by joining a sub-substrate to a main substrate with a through-hole, where the lower surface of the back chamber is closed, preventing bonding agent run-up and improving rigidity, thereby stabilizing vibration characteristics and enhancing sensitivity and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thermosetting bonding agent is used to bond the silicon substrate to the base substrate, then bonding strength is improved, but the bonding agent runs up the back chamber wall and invades the gap between the vibration electrode plate and silicon substrate, causing sensitivity degradation
Solution Approach 1:
The back chamber structure is segmented by introducing a protrusion that divides the internal space. This segmentation prevents the bonding agent from running up the entire wall surface and invading the gap between the vibration electrode plate and silicon substrate, thereby maintaining sensitivity while preserving bonding strength.
Solution Approach 2:
The protrusion acts as an intermediary structure within the back chamber that intercepts and blocks the bonding agent flow. This intermediate element prevents direct contact between the bonding agent and the critical gap area, resolving the conflict between bonding strength and sensitivity.
2Ease of manufacture
If an organic substrate is used instead of ceramic substrate to reduce cost, then manufacturing cost is improved, but thermal stress causes warpage and deformation of the silicon substrate
Solution Approach 1:
The protrusion structure changes the mechanical parameter distribution within the back chamber, providing additional structural support that compensates for the lower rigidity of organic substrates. This allows cost-effective organic substrates to be used while minimizing thermal stress-induced warpage and deformation.
3Manufacturing precision
If the vibration electrode plate is made thinner to increase sensitivity, then sensitivity is improved, but the plate becomes brittle and prone to breaking
Solution Approach 1:
The protrusion structure provides beforehand mechanical support and cushioning to the vibration electrode plate by preventing bonding agent invasion and reducing stress concentration. This allows the plate to be made thinner for higher sensitivity while the protrusion acts as a protective element that prevents brittle failure under impact.
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 prevents sensitivity degradation, improves impact resistance, and reduces the risk of substrate deformation, allowing for thinner vibration electrode plates and increased sensitivity while simplifying the production process and reducing costs.
Implementation Method 1
The acoustic vibration is converted into an electric signal and outputted based on an electrostatic capacitance change between the vibration electrode plate 18 and the fixed electrode plate 19
Implementation Method 2
The vibration electrode plate 18 vibrates by resonating with the acoustic vibration
Implementation Method 3
the bonding agent 24 that is in the fluidized state immediately after application runs up the wall surface of the back chamber 17 by a surface tension
Data Source
AI summary
An acoustic sensing element has a substrate that includes a back chamber, a vibration electrode plate that is provided in a surface of the substrate while being opposite an upper surface opening of the back chamber, and a fixed electrode plate that is provided opposite the vibration electrode plate, an acoustic hole being made in the fixed electrode plate. The acoustic sensing element outputs an electric signal based on an electrostatic capacitance change generated between the vibration electrode plate and the fixed electrode plate by a displacement of the vibration electrode plate. A lower surface of the back chamber is closed into a pouched shape by the substrate.