Thermal Flow Meter Integrated Sensor and Drive Circuit
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Solution Overview
Problem
Current thermal-type air flowmeters with semiconductor sensor elements have complex constructions due to separate mounting of chip capacitors and temperature detection elements, leading to increased costs and reduced reliability, while requiring faster responsiveness for automotive applications.
Innovation Solution
A thermal-type flowmeter with a simplified construction where the sensor element, drive circuit, chip capacitors, and chip thermistor are directly mounted on a metal lead frame and encapsulated with thermosetting resin, using gold bonding wires for electrical connections and a conductive adhesive to ensure conduction, with a relief in the molding process to prevent damage to the thin-film sensor element and a path for air expansion to maintain detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chip capacitors and temperature detection elements are separately mounted on ceramic substrates, then drive circuits are protected from noise, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent combines the sensor element, drive circuit, chip capacitors, and temperature detection element into a single integrated sensor unit. The drive circuit and sensor element are mounted on the same ceramic substrate, eliminating the need for separate mounting structures. This integration maintains noise protection through proper circuit layout and grounding while significantly reducing device complexity and the number of assembly steps.
Solution Approach 2:
The ceramic substrate serves multiple functions simultaneously: it acts as a mechanical support structure, an electrical connection platform, a noise shielding barrier, and a thermal management component. The chip capacitors are strategically positioned to provide both electrical decoupling and physical protection against electromagnetic interference, demonstrating multi-functionality that reduces overall device complexity.
2Speed
If semiconductor sensor elements with thin-film structures are used, then response speed and power consumption are improved, but mechanical stress and damage risk increase
Solution Approach 1:
The patent employs a multi-layer protective structure including a robust ceramic substrate with embedded stress-relief features, carefully designed mounting configurations that distribute mechanical loads, and protective encapsulation layers. These cushioning measures are built into the device architecture before the thin-film sensor element is subjected to operational stresses, preventing damage while maintaining the element's fast response characteristics.
Solution Approach 2:
The patent optimizes the mechanical parameters of the mounting structure, including substrate thickness, material composition, and bonding layer properties, to match the mechanical characteristics of the thin-film sensor element. By adjusting these parameters, the system achieves compatibility between the fragile thin-film component and the rigid ceramic substrate, reducing stress concentration and improving durability without compromising response speed.
3Measurement precision
If multiple components are mounted on separate substrates, then each component can be optimized independently, but manufacturing processes and assembly steps increase
Solution Approach 1:
The patent integrates the sensor element, drive circuit, and temperature detection element onto a single ceramic substrate, allowing all components to be mounted and connected in one assembly process. This eliminates multiple substrate handling, alignment, and bonding steps that would be required for separate substrates, significantly improving manufacturing efficiency while maintaining component optimization through careful layout design.
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 results in a highly accurate, reliable, and cost-effective thermal-type flowmeter with improved responsiveness and reduced mechanical stress on the thin-film sensor element, enhancing detection accuracy and simplifying production processes.
Implementation Method 1
an exothermic resistor is formed on an electrically insulating film several μm in thickness, formed on the cavity
Implementation Method 2
a temperature sensor (a temperature sensing resistor) is formed upstream, and downstream, respectively, in the vicinity of the exothermic resistor, and discrimination between down-flow and back-flow is possible according to a temperature differential method
Data Source
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AI summary
In order to provide a thermal-type flowmeter highly accurate, with high reliability, and simple in construction, while being available at a lower price, a thermal-type flowmeter as proposed includes a sub-path that takes in a fluid under measurement; a sensor element that measures a flow-rate of the fluid under measurement in the sub-path; a temperature detection element that detects a temperature of the fluid under measurement; a drive circuit that controls a heating temperature of the sensor element; and a protection circuit that protects the drive circuit from noise, a cavity being formed on a substrate of the sensor element, an exothermic resistor being provided on a thin-film part on the cavity through the intermediary of an electrically insulating film, and a flow rate being detected on the basis of temperature distribution in the thin-film part.