Copper Foil Surface Treatment for High Frequency Signal Transmission
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Solution Overview
Problem
Conventional copper foils face challenges in reducing surface roughness for high-frequency signal transmission while maintaining bonding strength, as reducing surface roughness leads to increased signal attenuation and decreased bonding reliability.
Innovation Solution
A method of manufacturing copper foils involving an electrolyzing process with arsenic-free electrolytic roughening and surface protection treatments, followed by a non-copper metal element surface treatment layer with controlled concentrations to enhance conductivity and maintain surface roughness, thereby reducing electrical loss without compromising bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If surface roughness of copper foil is reduced to reduce transmission loss, then electrical conductivity improves, but bonding strength between copper foil and substrate decreases
Solution Approach 1:
The copper foil structure is segmented into multiple functional layers: a base copper foil layer, a roughened layer with copper particles for bonding, and a surface treatment layer. This segmentation allows the roughened layer to provide bonding strength while the controlled surface treatment layer manages electrical properties, resolving the contradiction between transmission loss and bonding strength.
Solution Approach 2:
Different regions of the copper foil are given different properties: the interface region with the substrate has a roughened surface with copper particles for strong bonding, while the signal transmission surface has controlled roughness to minimize transmission loss. This local differentiation allows simultaneous optimization of both bonding strength and electrical conductivity.
2Strength
If surface roughness is increased to improve bonding strength, then bonding strength increases, but transmission loss increases
Solution Approach 1:
The copper foil is segmented into distinct functional zones: a roughened bonding layer at the substrate interface and a separately controlled signal transmission surface. This allows the bonding layer to have high roughness for strength while the transmission surface maintains lower roughness for reduced loss.
Solution Approach 2:
The roughness characteristic is localized to specific regions: the bonding interface has enhanced roughness with copper particles for strong adhesion, while the signal transmission surface has controlled, lower roughness to minimize skin effect and transmission loss.
3Reliability
If non-copper metal elements are added to improve surface treatment, then surface properties improve, but electrical conductivity decreases
Solution Approach 1:
The concentration of non-copper metal elements in the surface treatment layer is precisely controlled within specific ranges (e.g., zinc: 1-10 ppm, nickel: 1-5 ppm, chromium: 1-10 ppm). This parameter control ensures sufficient surface treatment quality for reliability while maintaining electrical conductivity by limiting the impact of these elements on electrical loss.
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 method improves copper foil purity and conductivity, reducing electrical loss during high-frequency signal transmission while maintaining bonding strength between the copper foil and substrate, addressing the limitations of conventional processes.
Implementation Method 1
a conventional copper foil is provided by forming a raw foil on the cathode wheel by electroplating
Implementation Method 2
producing a raw copper foil having a predetermined surface by an electrolyzing process
Implementation Method 3
performing a roughening treatment on the rough surface of the raw foil to form a plurality of copper particles on the rough surface of the raw foil
Implementation Method 4
as the frequency of transmission increases, the skin effect on the surface of the circuit becomes more pronounced. That is, the current in the conductor will be concentrated on the surface of the conductor, which leads to an increase of the resistance and delay of the signal
Data Source
AI summary
A manufacturing method of copper foil and circuit board assembly for high frequency transmission are provided. Firstly, a raw copper foil having a predetermined surface is produced by an electrolyzing process. Subsequently, a roughened layer including a plurality of copper particles is formed on the predetermined surface by an arsenic-free electrolytic roughening treatment and an arsenic-free electrolytic surface protection treatment. Thereafter, a surface treatment layer is formed on the roughened layer, and the roughened layer is made of a material which includes at least one kind of non-copper metal elements and the concentration of the non-copper metal elements is smaller than 400 ppm. By controlling the concentration of the non-copper elements, the resistance of the copper foil can be reduced.