Thermal Flow Meter Bent Lead Stress Absorption
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Solution Overview
Problem
The existing thermal flow meters face challenges with increased costs and reliability issues due to the need for additional components and stress concentration at connection points caused by temperature differences, which can lead to cracking and peeling of leads connected to the connector terminal.
Innovation Solution
A thermal flow meter design featuring a circuit package sealed by resin molding, with a bent outer lead fixed to the housing, allowing the bent portion to absorb stress from temperature differences and prevent cracking and peeling at connection points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bonding wire is used to connect the electric circuit and connector terminal, then the connection can accommodate temperature difference expansion, but the number of components increases and manufacturing cost increases
Solution Approach 1:
The patent merges the lead wire with the housing by directly connecting the lead to the connector terminal and fixing it to the housing, eliminating the separate bonding wire component. This integration reduces the number of components while maintaining the ability to accommodate temperature differences through the lead's flexibility.
Solution Approach 2:
The lead wire serves multiple functions: it provides electrical connection between the circuit and connector terminal, and simultaneously acts as a flexible element to accommodate thermal expansion and contraction. This multi-functionality eliminates the need for separate bonding wires.
2Device complexity
If a rigid lead is directly connected to the connector terminal, then the number of components decreases, but stress concentration occurs at the connection point due to temperature difference expansion causing crack and peeling
Solution Approach 1:
The patent applies local quality by making only the lead connection portion flexible while keeping the housing and other structures rigid. This localized flexibility at the lead-wire connection point allows stress absorption without compromising the overall structural integrity.
Solution Approach 2:
The flexible lead wire acts as a pre-designed stress absorption element that cushioning against thermal expansion forces before they can reach the rigid housing structure. This beforehand cushioning prevents stress concentration at critical connection points.
3Reliability
If additional components are added to accommodate stress from temperature differences, then connection reliability improves, but manufacturing cost increases
Solution Approach 1:
The patent combines the stress-accommodation function with the existing lead wire structure, eliminating the need for additional stress-absorption components. This merging reduces part count and manufacturing complexity while maintaining reliability.
Solution Approach 2:
The lead wire structure is designed to self-accommodate stress through its inherent flexibility, without requiring external active components or complex mechanisms. This self-service approach simplifies manufacturing while ensuring reliable stress management.
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 design enhances the thermal flow meter's ability to absorb stress from temperature differences, preventing cracking and peeling at connection points, thereby improving reliability and reducing costs by eliminating the need for additional components.
Implementation Method 1
an air flow sensing portion for measuring a flow rate of the measurement target gas by performing heat transfer with the measurement target gas flowing through the bypass passage
Implementation Method 2
a bent portion having a bent shape is provided on the outer lead... when a stress in the axial direction is applied to the lead due to a temperature difference between the housing and the circuit package, the bent portion deforms and can absorb the stress
Implementation Method 3
the housing expands or shrinks in the longitudinal direction, and when there is a change in the distance between the electric circuit and the connector terminal, the bonding wire is deformed
Data Source
AI summary
To obtain a thermal flow meter capable of alleviating stress in an axial direction that acts on a lead according to a temperature difference between a proximal end side and a leading end portion side of a measuring portion. An air flow sensing portion 300 according to the present invention includes a bypass passage for flowing a measurement target gas 30 received from a main passage 124, and an air flow sensing portion 602 for measuring a flow rate of the measurement target gas 30 by performing heat transfer with the measurement target gas 30 flowing through the bypass passage via a heat transfer surface, and the thermal flow meter includes a circuit package 400 in which the air flow sensing portion 602 and a lead 514 are sealed by a first resin molding process and a housing 302 forming a part of the bypass passage and fixing the circuit package 400 by a second resin molding process. The lead 514 has an outer lead 412 fixed to the housing 302 and protruding from the circuit package 400, and a bent portion 416 having a bent shape is provided on the outer lead 412.