Strain Gauge Electrode with Copper and Gold Layers
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Solution Overview
Problem
Strain gauges using chromium or nickel for resistors face poor solderability due to metallization dissolution and autoxidation of chromium, leading to reduced adhesion and tensile strength in connections.
Innovation Solution
A strain gauge design featuring a flexible substrate with a resistor made from chromium or nickel, and electrodes with a copper or nickel alloy metallic layer for improved solderability, along with a second metallic layer of gold or platinum for enhanced solder wettability, preventing metallization dissolution and oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If material including Cr (chromium) or Ni (nickel) is used for the resistor, then the resistor can be formed with appropriate electrical properties, but solderability of the electrode gets worse due to autoxidation and metallization dissolution
Solution Approach 1:
A copper layer is introduced as an intermediary between the chromium/nickel resistor and the solder. The copper layer serves as a protective barrier that prevents direct contact between the solder and the chromium/nickel metallization, thereby preventing dissolution and oxidation. This intermediary layer enables reliable soldering while preserving the electrical properties of the underlying resistor material.
Solution Approach 2:
The electrode structure is designed as a composite system with multiple layers: the base chromium or nickel layer provides electrical functionality, while the additional copper layer provides solderability. This composite structure combines the advantages of different materials - the electrical properties of Cr/Ni with the soldering properties of copper - to achieve both reliable electrical connection and good solderability.
2Device complexity
If both ends of the resistor are used as electrodes, then the structure is simplified, but dissolution of metallization easily occurs due to thin film thickness, resulting in less solderability
Solution Approach 1:
The thin-film electrode is enhanced by adding a copper layer to create a composite structure. This maintains the simplified single-ended electrode configuration while compensating for the thinness-induced dissolution problem through the protective and solder-receptive copper overlay.
Solution Approach 2:
The copper layer acts as an intermediary that protects the thin chromium/nickel film from direct exposure to solder. This prevents dissolution of the thin metallization while maintaining the simplified electrode structure where both ends of the resistor serve as electrodes.
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 significantly improves solderability and prevents metallization dissolution, ensuring strong adhesion and reliable connections for strain gauges using chromium or nickel resistors.
Implementation Method 1
a second metallic layer formed of material having better solder wettability than the first metallic layer, on or above the first metallic layer
Implementation Method 2
a second metallic layer formed of material having better solder wettability than the first metallic layer
Data Source
AI summary
A strain gauge includes a flexible substrate; a resistor formed of material including at least one from among chromium and nickel, on or above the substrate; and electrodes electrically coupled to the resistor. Each electrode includes a terminal section extending from a corresponding end portion from among end portions of the resistor; a first metallic layer formed of copper, a copper alloy, nickel, or a nickel alloy, on or above the terminal section; and a second metallic layer formed of material having better solder wettability than the first metallic layer, on or above the first metallic layer.