Electrochemical Copper Deposition with Dual Current Density for Glossy RA Foil
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Solution Overview
Problem
The challenge is to achieve a shiny or glossy surface appearance for copper layers in flexible printed circuit boards produced using rolled and annealed (RA) copper foils, which typically result in a matte surface due to their macro-scale inhomogeneous structure, affecting automated optical inspection and subsequent processing steps.
Innovation Solution
A process involving electrochemical copper deposition with alternating current densities, starting with a high initial current density for a short period to form a thin barrier layer and then reducing the current density for the remainder of the deposition time to ensure uniform copper distribution and filling of structures without defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If low current density is used for filling structures like blind micro vias and through holes, then structure filling is achieved, but the surface appearance becomes matte
Solution Approach 1:
The electrochemical deposition process is divided into multiple stages with different current densities. The first stage uses high current density to build up copper and create a shiny surface, while the second stage uses low current density to fill structures. This temporal segmentation allows both surface quality and structure filling to be optimized independently.
Solution Approach 2:
The high current density deposition is performed first as a preliminary action to establish a shiny surface morphology. Only after this surface layer is formed does the process transition to low current density for structure filling, ensuring the surface appearance is established before the filling operation begins.
2Illumination intensity
If high current density is applied during electrochemical copper deposition, then shiny surface appearance is achieved, but structure filling becomes insufficient
Solution Approach 1:
The current density is made dynamic rather than static, transitioning from high to low values during the deposition process. This dynamic adjustment allows the system to adapt its deposition rate and morphology control throughout the process, achieving both shiny surfaces and complete structure filling.
Solution Approach 2:
The electrochemical deposition employs periodic changes in current density with distinct high-current phases for surface quality and low-current phases for structure filling. This periodic modulation of deposition parameters enables the system to alternately optimize for surface appearance and structure penetration.
3Adaptability or versatility
If RA copper foil with macro-scale inhomogeneous surface is used, then flexibility is improved, but surface uniformity after etching deteriorates
Solution Approach 1:
The electrochemical deposition parameters (current density, time) are changed to compensate for the underlying surface inhomogeneity. By using high current density initially, the process overwrites the macro-scale variations from the RA foil etching, creating a uniform shiny surface that masks the substrate irregularities.
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 method produces copper surfaces with a glossiness of at least 400 Gloss Units, enhancing inspection and processing capabilities, and allows for blister-free, thick electroless copper deposits, especially in critical areas like blind micro vias and exposed adhesive layers.
Implementation Method 1
depositing copper by electroless copper deposition on the first etched surface, thereby creating a first electroless copper layer on the first etched surface
Implementation Method 2
depositing further copper by electrochemical deposition on the first electroless copper layer, thereby creating a first electrochemical copper layer
Data Source
Figure 1~2
Figure 3
AI summary
A process for electrochemical deposition of copper, comprising - providing a rolled and annealed copper foil comprising a first surface and a second surface, - etching the first surface of the rolled and annealed copper foil, thereby creating a first etched surface, - depositing copper by electroless copper deposition on the first etched surface, thereby creating a first electroless copper layer on the first etched surface, - depositing further copper by electrochemical deposition on the first electroless copper layer, thereby creating a first electrochemical copper layer, wherein in the electrochemical deposition in a first period of time a first current density is applied and in a second period of time a second current density is applied, wherein the second current density is lower than the first current density, and a layered product obtainable by the process. (Fig. 3)