Roughened Copper Foil Surface Profile for Transmission Loss and Powdering
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Solution Overview
Problem
Existing copper foils used in printed wiring boards face challenges in achieving both excellent transmission characteristics for high-frequency applications and preventing powdering due to micro-roughening treatments, which often lead to detachment of roughening particles.
Innovation Solution
A roughened copper foil with a controlled roughness slope tan θ of 0.58 or less and a sharpness index Rc×Sku of 2.35 or less, calculated based on specific surface profile parameters, is developed to enhance transmission characteristics while suppressing powdering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If micronization of roughening particles is performed to suppress skin effect, then transmission loss is reduced, but roughening particles detach due to physical contact
Solution Approach 1:
The invention changes the geometric parameters of the roughening particles by controlling both the particle size distribution (D10, D50, D90 values) and the shape factor (sphericity ψ). By optimizing these parameters together - using particles with 10-250 nm size range and specific shape factors - the invention achieves low transmission loss while preventing particle detachment, resolving the technical contradiction between energy loss reduction and reliability improvement
2Strength
If roughening treatment is applied to improve adhesion, then bonding strength increases, but transmission characteristics deteriorate due to increased conductor loss
Solution Approach 1:
The invention applies local quality by creating roughening particles with specific local geometric characteristics (size distribution and shape factor) that differ from conventional uniform particles. This localized optimization of particle properties allows the surface to provide both anchoring function for adhesion and controlled electromagnetic interaction for low conductor loss, resolving the contradiction between strength and energy 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 controlled surface roughness and sharpness index effectively improve transmission characteristics and prevent powdering, ensuring high peel strength and reliable performance in high-frequency applications.
Implementation Method 1
The conductor loss can be increased by a skin effect of a copper foil that appears more remarkably as the frequency increases
Implementation Method 2
the bonding surface of the copper foil is subjected to roughening treatment to form irregularities composed of fine copper particles, and these irregularities are allowed to bite into an insulating resin substrate by pressing to exhibit an anchor effect to improve the adhesion
Data Source
AI summary
Provided is a roughened copper foil capable of achieving both excellent transmission characteristics and suppression of powdering. This roughened copper foil includes a roughened surface on at least one side. The roughened surface has a roughness slope tan θ of 0.58 or less as calculated based on a mean height Rc (μm) and a mean width RSm (μm) of profile elements by formula Rc/(0.5×RSm), and a sharpness index Rc×Sku of 2.35 or less that is a product of the mean height Rc (μm) and a kurtosis Sku. Rc and RSm are values measured in accordance with JIS B0601-2013 under a condition of not performing a cutoff by a cutoff value λs and a cutoff value λc, and Sku is a value measured in accordance with ISO 25178 under a condition of not performing a cutoff using an S filter and an L filter.