Anisotropic Etching of PCB Copper for Vertical Conductor Tracks
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Solution Overview
Problem
Conventional isotropic copper etching processes in printed circuit board manufacturing result in undercuts and poor adhesion due to horizontal etching, limiting the ability to form fine structures and comply with miniaturization requirements.
Innovation Solution
An anisotropic etching process using a sequence of three distinct etching compositions, including an etchant and etching inhibitor, followed by a pH-adjusted composition to selectively remove the inhibitor from the bottom surface, and finally an etchant-free composition to promote vertical etching, resulting in conductor tracks with substantially vertical side walls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If isotropic etching is used, then the etching process is simple and can be easily implemented, but undercuts are formed beneath the mask resulting in poor adhesion and inability to form fine structures
Solution Approach 1:
The etching process is divided into multiple sequential steps using different etching compositions. The first composition creates initial etching with undercut control, the second composition selectively removes the undercut portion, and the third composition completes the vertical etching. This segmentation transforms a single isotropic etching step into a multi-step process that achieves anisotropic results.
Solution Approach 2:
The invention changes the chemical parameters by using different etching compositions with varying properties. The first composition contains etchant and inhibitor in specific ratios to control initial etching, the second composition has different chemical properties to selectively remove undercuts, and the third composition completes the vertical etching. These parameter changes enable precise control over etching direction and structure formation.
2Manufacturing precision
If anisotropic etching is used to form fine structures with vertical side walls, then manufacturing precision is improved, but the process complexity increases with multiple etching compositions and steps
Solution Approach 1:
Multiple etching functions are merged into a coordinated sequence of three compositions working together. The first composition performs initial etching and undercut formation, the second composition selectively removes undercuts while preserving vertical walls, and the third composition completes the etching. This merging of functions into a standardized process sequence achieves complex anisotropic etching through coordinated simple steps.
Solution Approach 2:
The first etching composition acts as an intermediary by creating controlled undercuts that serve as a foundation for the second composition. These undercuts are intentionally formed as an intermediate state that allows the second composition to selectively remove horizontal portions while leaving vertical portions intact, ultimately achieving the desired anisotropic structure.
3Productivity
If conventional single-step etching is used, then productivity is maintained with a single process step, but the quality of conductor tracks deteriorates with irregular shapes and poor adhesion
Solution Approach 1:
The etching process is segmented into three distinct compositions, each performing a specific function: initial etching with undercut control, selective undercut removal, and completion of vertical etching. This segmentation allows each step to be optimized for its specific purpose while maintaining overall process efficiency through standardized sequential execution.
Solution Approach 2:
Chemical parameters are changed between steps by using different etching compositions with varying etchant-to-inhibitor ratios and chemical properties. The first composition uses specific parameters for initial etching, the second composition uses different parameters for selective undercut removal, and the third composition uses optimized parameters for completing the vertical structure, ensuring high conductor track quality.
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 process enhances the quality of printed circuit boards by reducing defects, improving etching homogeneity, and enabling line widths below 50 µm, such as 30 µm or less, while maintaining regular shape and adhesion.
Implementation Method 1
subjecting the electrically conductive layer structure to a first etching composition forming a recess having a bottom surface and side wall surfaces
Implementation Method 2
the first etching composition comprises an etchant and an etching inhibitor
Implementation Method 3
the second etching composition is configured for selectively removing the etching inhibitor and/or an inhibition layer formed after applying the first etching composition from the bottom surface of the recess rather than from the wall surfaces
Data Source
Figure 1~2
Figure 3~4
Figure 5A~5C
AI summary
A method of etching an electrically conductive layer structure of a component carrier for forming a conductor track is provided, wherein the method comprises the steps of subjecting the electrically conductive layer structure to a first etching composition, and subsequently subjecting the electrically conductive layer structure to a second etching composition being different from the first etching composition. In addition, an apparatus for etching an electrically conductive layer structure, a conductor track, an arrangement of at least two conductor tracks, and a component carrier are provided.