Thermal Air Flow Meter Substrate Filler Design
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Solution Overview
Problem
The existing thermal air flow meters face challenges in achieving high measurement accuracy due to variations in the position and angle of the sensor assembly caused by the adhesive used for fixing, which also leads to thermal stress and reduced accuracy from heat generated in electronic components.
Innovation Solution
The thermal air flow meter integrates a sensor assembly with a ceramic or printed substrate, where the electronic components are covered with a filling material like epoxy resin to enhance heat dissipation and protect from environmental exposure, and the substrate and filling material's coefficients of linear expansion and Young's modulus are optimized to minimize thermal stress and maintain accuracy within ±1%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If adhesive is used to fix the sensor assembly to the housing, then assembly is simplified and parts are easily replaced, but measurement accuracy deteriorates due to position and angle variations
Solution Approach 1:
The device is divided into a housing and a separately manufacturable sensor assembly. The sensor assembly includes a sensor chip mounted on a substrate, which can be manufactured and tested independently before being installed in the housing. This segmentation allows for simplified assembly while maintaining measurement accuracy through precise positioning features built into the sensor assembly structure itself.
2Temperature
If electronic components are exposed, then heat dissipation is improved, but reliability deteriorates due to environmental exposure to exhaust gases and salt water
Solution Approach 1:
A protective coating or encapsulation layer is applied to the electronic components and sensor assembly. This thin protective film barriers exhaust gases, salt water, and other environmental contaminants from contacting the sensitive electronics, while still allowing heat to dissipate from the components. The coating maintains reliability by preventing corrosion and contamination.
3Stability of the object's composition
If thermal mass is increased for better temperature stability, then temperature stability improves, but response time deteriorates
Solution Approach 1:
The housing and sensor assembly incorporate thermal mass elements strategically positioned to provide temperature stability only where needed - specifically in the regions surrounding the sensor chip and electronic components. The thermal mass is not uniformly distributed throughout the entire device, but rather concentrated in localized areas that benefit from thermal buffering, while other areas maintain rapid thermal response.
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 configuration improves measurement accuracy by reducing thermal stress and maintaining flow rate detection precision, even under varying temperature conditions and environmental exposures, such as exhaust gases and salt water, while preventing electronic component exposure.
Implementation Method 1
a flow rate detection unit that measures the flow rate of gas through heat transfer between the flow rate detection unit and the gas to be measured
Implementation Method 2
electronic components are covered with a filling material like epoxy resin to enhance heat dissipation
Data Source
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AI summary
The purpose is to improve the measurement accuracy of a thermal air flow meter. The device has: an auxiliary passage for entraining a portion of a fluid being measured; a sensor chip arranged in the auxiliary passage, for measuring the flow rate of the fluid being measured; an electronic component having an internal resistor, for converting the fluid flow rate detected by the sensor chip to an electrical signal; and a substrate on which the sensor chip and the electronic component are mounted. The substrate is covered by a filler material, on the surface of which the electronic component is mounted.