Copper Foil Surface Gradient Control for Low-Loss Flexible PCBs
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Solution Overview
Problem
Current copper foils for high-frequency circuits face significant conduction loss due to the skin effect, particularly at frequencies above 10 GHz, where existing surface roughening techniques struggle to maintain low conduction loss while ensuring adequate adhesion to resin substrates.
Innovation Solution
The copper foil is treated to achieve a root mean square gradient (Sdq) of 0.120 or less on its surface, which suppresses conduction loss by minimizing surface unevenness, and may optionally include a surface treatment layer with magnetic metals to enhance conductivity and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If surface roughening treatment is applied to copper foil, then adhesion to resin substrate is improved, but conduction loss increases due to skin effect
Solution Approach 1:
The patent applies parameter changes by precisely controlling the root mean square gradient (Sdq) of the copper foil surface to 0.120 or less, and controlling the thickness and composition of the surface treatment layer. This optimization allows achieving adequate adhesion while minimizing surface roughness to reduce conduction loss at high frequencies.
Solution Approach 2:
The patent implements local quality by applying a surface treatment layer with magnetic metals selectively on the copper foil surface. This creates a localized functional layer that provides both adhesion enhancement and conductivity improvement without requiring the entire surface to be roughened, thus reducing overall conduction loss.
2Reliability
If surface treatment layer with magnetic metals is added, then conductivity is enhanced, but surface complexity increases
Solution Approach 1:
The patent uses composite materials by combining copper foil with a surface treatment layer containing magnetic metals. This composite structure leverages the high conductivity of copper and the beneficial magnetic properties of the surface layer to enhance overall conductivity while managing surface complexity through controlled layering.
Solution Approach 2:
The patent controls the thickness and composition parameters of the surface treatment layer to optimize conductivity enhancement. By precisely adjusting these parameters, the patent achieves improved conductivity without excessive surface complexity that would complicate manufacturing or performance.
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 approach effectively reduces conduction loss at high frequencies, maintaining low resistance and ensuring strong adhesion to resin substrates, even with surface treatments, thereby improving the performance of high-frequency circuit boards.
Implementation Method 1
In high frequency signals, the main cause of conductor loss is that the cross-sectional area through which current flows decreases due to the skin effect, that is, the higher the frequency is, the more current flows only on the surface of the conductor, and the resistance increases.
Implementation Method 2
The copper foil may optionally include a surface treatment layer with magnetic metals to enhance conductivity and adhesion
Data Source
Figure 1
AI summary
A copper foil, wherein at least one surface of the copper foil has a root mean square gradient (Sdq) of 0.120 or less.