Flexible Strain Gauge Substrate Surface Finish Control

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Solution Overview

Problem

Strain gauges with resistors formed on flexible substrates often experience pinhole generation, leading to deteriorated gauge characteristics when the number of pinholes exceeds a predetermined value.

Innovation Solution

Reducing surface unevenness on the substrate to 15 nm or less, either through heat treatment or other methods like laser irradiation or polishing, ensures that the number of pinholes in the resistor is minimized, thereby maintaining stable gauge characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a resistor is formed on a flexible substrate, then the strain gauge can be applied to flexible surfaces, but pinholes are generated in the resistor leading to deteriorated gauge characteristics

Engineering Contradiction:

ImproveflexibilityVSAvoidgauge characteristics

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The substrate surface is pre-treated before resistor formation to reduce surface unevenness to 15 nm or less. This preliminary action prevents pinhole generation during subsequent resistor deposition, thereby maintaining gauge characteristics while preserving substrate flexibility.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The surface roughness parameter of the substrate is changed from a higher value to 15 nm or less through heat treatment or other surface processing methods. This parameter change eliminates pinhole formation in the resistor layer while maintaining the flexible nature of the substrate.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If surface unevenness on the substrate is reduced to 15 nm or less, then the number of pinholes in the resistor is minimized, but additional processing steps are required

Engineering Contradiction:

Improvesurface unevennessVSAvoidprocessing steps

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

Heat treatment is applied to the substrate to change its physical state and reduce surface unevenness to 15 nm or less. This thermal processing method achieves the required surface precision without requiring multiple mechanical processing steps.

Inventive Principle:

Principle #35Parameter changes

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 reduction in pinholes results in improved gauge characteristics and stable strain gauge performance, with the resistor's thickness of 0.05 um or more effectively preventing deterioration, even with substrates containing fillers.

Implementation Method 1

Reducing surface unevenness on the substrate to 15 nm or less, either through heat treatment or other methods like laser irradiation or polishing

Methodology Applied

Scientific EffectHeat treatment: Heat Treatment

Implementation Method 2

Reducing surface unevenness on the substrate to 15 nm or less, either through heat treatment or other methods like laser irradiation or polishing

Methodology Applied

Scientific EffectLaser irradiation: Laser

Data Source

PatentEP3690388B1Strain gauge

Publication Date: 2023.09.20 MINEBEAMITSUMI INC

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AI summary

A strain gauge includes a flexible substrate, and a resistor formed of material including at least one from among chromium and nickel, on or above the substrate. Surface unevenness on one surface of the substrate is 15 nm or less, and the resistor has a film thickness of 0.05 µm or more.