Flexible Circuit Inner Leads With Dummy Lines for Uniform Etching
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Solution Overview
Problem
Conventional flexible circuit boards experience nonuniform etching of inner leads due to varying spaces between bumps on chips, leading to inconsistent etching speeds and irregular shapes like trapezoidal cross-sections.
Innovation Solution
Incorporating dummy lines in larger spaces between inner leads to ensure uniform etching by dividing them into smaller spaces of equal or less than 50 um, with dummy lines occupying less than 0.5% of total spaces, allowing consistent etching solution flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If inner leads are arranged with different intervals to match bump patterns, then adaptability to chip designs is improved, but etching uniformity deteriorates causing nonuniform inner lead widths and trapezoidal shapes
Solution Approach 1:
The patent introduces dummy lines as intermediary elements between inner leads with larger intervals. These dummy lines act as mediators that modify the etching solution flow path, ensuring uniform etching speed across all spaces. The dummy lines are designed with specific width ratios (0.5-2 times the inner lead width) and positioned strategically to balance the etching process without affecting the electrical functionality of the inner leads.
Solution Approach 2:
The patent changes the physical parameters of the etching process by introducing additional structures (dummy lines) that alter the flow dynamics of the etching solution. By controlling the width, length, and position parameters of the dummy lines, the etching speed distribution is optimized to achieve uniform inner lead widths despite varying intervals between bumps and inner leads.
2Productivity
If etching solution flows through spaces with different distances, then productivity is improved by processing varied intervals, but manufacturing precision deteriorates due to inconsistent etching speeds
Solution Approach 1:
Dummy lines serve as intermediary structures that equalize the etching solution flow path lengths across different spaces. By introducing these mediators, the patent maintains the ability to process varied intervals (productivity) while ensuring that the effective etching distance is standardized, resulting in consistent inner lead widths (precision).
Solution Approach 2:
The patent segments the etching spaces by introducing dummy lines that divide larger spaces into effective etching zones. This segmentation allows the etching process to handle varied intervals efficiently while maintaining uniform etching characteristics within each segmented zone, thereby preserving both productivity and precision.
3Adaptability or versatility
If spaces between inner leads are larger than 50 um, then adaptability to bump patterns is improved, but etching uniformity deteriorates causing trapezoidal cross-sections
Solution Approach 1:
Dummy lines are introduced as intermediary elements in spaces larger than 50 um between inner leads. These mediators extend the etching solution path length, ensuring that even in larger spaces, the etching speed remains consistent with smaller spaces. This prevents the formation of trapezoidal cross-sections and maintains rectangular shapes, while still allowing flexible bump arrangements.
Solution Approach 2:
The patent addresses the two-dimensional spacing issue by introducing elements that extend into another dimensional aspect of the etching process (the flow path dimension). By controlling the etching solution path length through dummy lines, the patent effectively transforms the problem from a simple distance-based issue to a path-length-based solution, maintaining uniform cross-sectional shapes regardless of the planar distance between inner leads.
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
Ensures uniform etching of inner leads, preventing irregular shapes and maintaining mechanical integrity by controlling etching speeds and distances, thus producing rectangular cross-sections.
Implementation Method 1
The circuit lines are usually formed on the flexible substrate through wet etching. An etching solution is running to etch a metal layer not covered by a patterned photoresist
Data Source
AI summary
An inner lead structure of a flexible circuit board includes a flexible substrate, a circuit layer and a dummy circuit layer. A chip mounting area defined on the flexible substrate is provided for a chip, contacting locations defined within the chip mounting area are provided for conductive elements of the chip. The circuit layer includes inner leads, ends of the inner leads are arranged on the contacting locations and provided to be electrically connected to the conductive elements. At least one of first dummy lines of the dummy circuit layer is arranged in a space between the adjacent inner leads. The space having a distance greater than 50 um is divided into multiple spaces having distances not greater than 50 um. Proportion of the spaces without the first dummy lines and having a distance greater than 50 um is less than 0.5% in all spaces.