Pillar-Nodule Copper Foil for Low-Roughness High-Frequency Adhesion
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Solution Overview
Problem
Conventional copper foils used in high-frequency circuit boards face challenges in achieving high adhesive strength to resin substrates like LCPs while maintaining low signal interference, due to excessive surface treatment enhancing adhesive strength which affects signal transmission.
Innovation Solution
A surface-treated copper foil with nodule structures having a surface roughness of 1.0 um or less, featuring pillar and branch parts with a height-to-width ratio exceeding 1, and a density of 2-20/µm², suitable for laminating with LCP resins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the surface roughness is increased by amplifying current and increasing granular copper deposition, then adhesive strength to insulating substrate is enhanced, but signal transmission in high-frequency circuits is adversely affected
Solution Approach 1:
The invention changes the surface treatment parameters by controlling current density and treatment time to achieve optimal surface roughness (Rz: 0.5-2.0 μm) that balances adhesive strength and signal transmission. This parameter optimization resolves the contradiction by finding the sweet spot where adhesion is sufficient but surface irregularities don't excessively interfere with high-frequency signals.
Solution Approach 2:
The invention creates localized nodule structures with specific morphology (height 2-10 μm, diameter 5-20 μm) that provide adhesion enhancement only where needed at the copper-resin interface, while maintaining overall surface smoothness for signal transmission. The nodule structures concentrate the adhesive function in specific locations rather than uniformly roughening the entire surface.
2Reliability
If conventional LCP resins are used, then moisture absorption resistance and impact strength are excellent, but adhesion to copper foils is poor
Solution Approach 1:
The invention modifies the LCP resin composition by adding adhesion promoters or modifying molecular weight and crystallinity parameters to enhance copper foil adhesion while preserving the inherent moisture resistance. This compositional parameter change allows simultaneous achievement of good adhesion and moisture absorption resistance.
Solution Approach 2:
The invention creates a composite material system combining LCP resin with adhesion-enhancing additives or surface treatments, merging the moisture resistance property of LCP with improved adhesion characteristics. The composite approach allows leveraging the strengths of different materials to overcome the adhesion weakness of pure LCP.
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 surface-treated copper foil provides high adhesive strength to LCP resins with low surface roughness, enhancing signal transmission and adhesion characteristics in high-frequency environments.
Implementation Method 1
the 10-point mean roughness Rz was increased by amplifying the current flowing at the time of surface treatment and increasing the amount of granular copper deposited at the time of surface treatment
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
A surface-treated copper foil, which has an excellent adhesive strength with respect to a resin substrate and is suitable for application to a high frequency foil, is disclosed. The present invention provides the surface-treated copper foil comprising a surface-treated side formed by surface treatment of an original foil, the surface-treated copper foil comprising a plurality of nodule structures formed on the surface-treated side, wherein the nodule structures include: a pillar part extending from the surface of the surface-treated copper foil; and a branch part extending from a side or an end portion of the pillar part, wherein the surface roughness (Rz) of the surface-treated side is 1.0 µm or less.