Rolled Copper Foil Grain Control for Flex Fatigue
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Solution Overview
Problem
Conventional rolled copper foils used in flexible flat cables are prone to early breaking under high temperature environments due to work strain, have high production costs, and inadequate grain size for flexing characteristics and strength.
Innovation Solution
A rolled copper foil with crystal particles of copper or copper alloy, where the average particle size of the outermost surface is between 0.2 µm and 6 µm, and the intragranular distortion rate is between 0.5% and 10%, suppressing crack generation under repeated flexion deformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional rolled copper foil with work strain is used, then manufacturing cost is reduced, but the copper foil is susceptible to early breaking during flex fatigue under high temperature environments
Solution Approach 1:
The patent changes the crystal grain size parameter to between 5-30 μm and controls the texture composition (cube texture ratio of 30-80%) to eliminate work strain while maintaining manufacturing feasibility. This resolves the contradiction by finding optimal parameter ranges that provide both reliability and ease of manufacture.
2Ease of operation
If cube texture is extremely developed by sequential cold rolling and annealing, then flexing characteristics are improved, but manufacturing cost increases and average grain size becomes too large
Solution Approach 1:
The patent optimizes the cube texture ratio to 30-80% rather than extreme development, and controls grain size to 5-30 μm. This balanced parameter selection maintains good flexing characteristics while reducing manufacturing cost and avoiding excessive grain growth.
3Ease of manufacture
If average grain size is increased to 5-30 μm, then manufacturing cost is reduced, but flexing characteristics and strength become inadequate
Solution Approach 1:
The patent specifies a grain size range of 5-30 μm combined with controlled cube texture (30-80%) to achieve the optimal balance between manufacturing cost and flexing strength. This parameter optimization ensures both economic viability and mechanical performance.
4Temperature
If conductor strength is increased to 350-400 MPa, then high temperature environment resistance is improved, but work strain remains and early breaking occurs during flex fatigue
Solution Approach 1:
The patent changes the crystal grain size to 5-30 μm and controls texture composition to eliminate work strain while maintaining adequate strength. This resolves the contradiction by showing that strength alone is not sufficient; grain size and texture control are needed to prevent flex fatigue failure.
Data Source
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Figure 3(a)~3(d)
AI summary
A rolled copper foil composed of crystal particles of copper or a copper alloy, wherein an average particle size of the crystal particles composing the outermost surface is not less than 0.2 µm and not greater than 6 µm; a ratio of the average particle size of the crystal particles composing the outermost surface to a thickness of the rolled copper foil is not less than 1% and not greater than 6%; and an intragranular distortion rate found by the following formula (1) when a cross-section perpendicular to a length direction of the rolled copper foil is analyzed by electron backscatter diffraction (EBSD) is not less than 0.5% and not greater than 10%. Intragranular distortion rate % = A / B x 100 (In the above formula (1), (A) represents the area of a region identified through image analysis to have an orientation difference of not less than 1 degree and not greater than 15 degrees, and (B) represents the area of a region identified through image analysis to have an orientation difference of not less than 0 degrees and not greater than 15 degrees).