Carrier-Attached Copper Foil Etching Uniformity
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Solution Overview
Problem
The formation of printed wiring boards with ultra-thin copper layers faces challenges in achieving uniformity due to chemical etching, which affects circuit accuracy and adhesion with dry films, leading to non-uniform thickness and excessive etching.
Innovation Solution
A carrier-attached copper foil with a controlled number of crystal grains per unit cross-sectional area and surface roughness is developed, featuring a carrier, an intermediate layer, and an ultra-thin copper layer, where the number of crystal grains is between 0.1 to 5 grains/μm² and the ten-point average roughness (Rz) is between 0.1 to 2.0 μm, improving etching uniformity and circuit formability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If chemical etching treatment is performed on the ultra-thin copper layer to roughen the surface for adhesion with dry film, then adhesion is improved, but the thickness uniformity deteriorates due to preferential etching at crystal grain boundaries
Solution Approach 1:
The patent applies parameter changes by controlling the crystal grain size of the copper layer to be 5 μm or less, which fundamentally alters the etching behavior. This grain size control prevents excessive etching at grain boundaries while still allowing sufficient roughening for adhesion, thus resolving the contradiction between adhesion improvement and thickness uniformity maintenance
Solution Approach 2:
The patent implements preliminary action by performing the chemical etching treatment with controlled parameters before applying the dry film. The etching is performed under controlled conditions (using ammonium persulfate solution at controlled temperature and time) to pre-roughen the surface adequately, preventing the need for aggressive etching that would compromise thickness uniformity
2Length of moving object
If the copper foil thickness is reduced to 9 μm or smaller to achieve finer pitch, then the pitch is reduced, but the handling ability deteriorates in lamination and casting processes
Solution Approach 1:
The patent applies composite materials by creating a multi-layer structure consisting of the ultra-thin copper layer (5 μm or less) combined with the polymer layer (thickness 1-10 μm). This composite structure provides the benefits of ultra-thin copper for fine pitch while the polymer layer provides mechanical strength and handling ability, resolving the contradiction between reduced pitch and maintained ease of operation
3Use of energy by moving object
If excessive etching occurs at crystal grain boundaries during chemical etching, then surface roughness increases for adhesion, but circuit accuracy deteriorates due to non-uniform thickness
Solution Approach 1:
The patent applies parameter changes by strictly controlling the crystal grain size to be 5 μm or less and using specific etching solutions (ammonium persulfate) under controlled conditions. This prevents excessive etching at grain boundaries while maintaining sufficient surface roughness for adhesion, thus resolving the contradiction between adhesion improvement and circuit accuracy maintenance
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 solution enhances the uniformity of chemical etching and improves circuit formability, ensuring better adhesion and accuracy in the formation of printed wiring boards, particularly for finer pitches and higher frequency applications.
Implementation Method 1
chemical etching treatment is performed on the ultra-thin copper layer to roughen a surface of the ultra-thin copper layer
Implementation Method 2
heating and pressuring the resultant (lamination process)
Implementation Method 3
heating and pressuring the resultant (lamination process)
Implementation Method 4
heating and curing the resultant (casting process)
Data Source
AI summary
A carrier-attached copper foil having good circuit formability is provided. The carrier-attached copper foil has a carrier, an intermediate layer and an ultra-thin copper layer in this order, the number of crystal grains per unit cross-sectional area of the ultra-thin copper layer in the through-thickness direction is 0.1 to 5 grains/μm2, and a ten point average roughness Rz of a surface on a side of the ultra-thin copper layer is 0.1 to 2.0 μm.