Electrolytic Copper Foil Crystal Structure for Flexible Substrates
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Solution Overview
Problem
Electrodeposited copper foils for flexible substrates face challenges in achieving both high smoothness and flexibility, particularly after annealing, as they tend to retain higher tensile strength and lower flexibility compared to rolled copper foils.
Innovation Solution
The electrodeposited copper foil features a high proportion of vertically long columnar crystals, as analyzed by electron backscatter diffraction (EBSD), with specific crystal orientation, aspect ratio, and angle conditions, resulting in a ten-point average roughness of 0.1 μm to 2.0 μm, which enhances both smoothness and flexibility suitable for flexible substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If electrodeposited copper foil is annealed to reduce tensile strength and increase flexibility, then flexibility improves, but tensile strength remains relatively high compared to rolled copper foil
Solution Approach 1:
The patent applies parameter changes by controlling the crystal grain structure through specific electrodeposition parameters (current density, temperature, electrolyte composition) to create a dominant (100) orientation with controlled aspect ratio. This structural parameter change enables the copper foil to achieve both low tensile strength (high flexibility) after annealing while maintaining smoothness, resolving the contradiction between flexibility and strength.
2Manufacturing precision
If the surface roughness is reduced to achieve high smoothness, then smoothness improves, but the ability to regulate tensile strength after annealing deteriorates
Solution Approach 1:
The patent changes the structural parameters by controlling crystal grain aspect ratio (0.5 or less) and orientation ((100) dominant) through electrodeposition. This enables simultaneous achievement of smooth surface (Rz ≤ 2.0 μm) and regulatable tensile strength after annealing, resolving the contradiction between smoothness and strength regulation capability.
Solution Approach 2:
The patent applies preliminary action by establishing the desired crystal grain structure (aspect ratio ≤ 0.5, (100) orientation) during the electrodeposition process before annealing. This pre-established structure enables subsequent annealing to effectively reduce tensile strength while maintaining smoothness, allowing tensile strength regulation to be achieved even with a smooth surface.
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
This structure allows for high flexibility after annealing at 180°C for 1 hour while maintaining low roughness, effectively balancing smoothness and flexibility, making it suitable for flexible substrates.
Implementation Method 1
in cross-sectional analysis by electron backscatter diffraction (EBSD), a proportion of an area occupied by copper crystal grains satisfying all of the following conditions
Implementation Method 2
high flexibility after annealing at 180° C. for 1 hour
Data Source
AI summary
Provided is an electrodeposited copper foil having high smoothness and exhibiting high flexibility (particularly, high flexibility after annealing at 180° C. for 1 hour) suitable for a flexible substrate. This electrodeposited copper foil has an Rz of 0.1 to 2.0 μm on at least one surface. In cross-sectional analysis by EBSD, a proportion of an area occupied by copper crystal grains satisfying the following conditions relative to an area of an observation field occupied by copper crystal grains is 63% or more. The conditions are as follows: i) (101) orientation; ii) an aspect ratio of 0.500 or less; iii) |sin θ| of 0.001 to 0.707, where θ (°) is an angle between a normal line of an electrode surface of the electrodeposited copper foil and a major axis of the copper crystal grain; and iv) when the crystal is elliptically approximated, a length of a minor axis of 0.38 μm or smaller.