Flexible Circuit Board Tin Layer Leveling
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Solution Overview
Problem
Existing flexible circuit boards face issues with bendability and stress accumulation due to increased thickness of dual solder resist layers and apparent height differences in tin layers, which can lead to cracking and complications in processing.
Innovation Solution
A novel flexible circuit board design featuring a thin tin layer in the bendable region to protect the conductive copper layer and maintain flexibility, with surfaces of the tin layers being level to prevent stress accumulation, and varying copper thicknesses in different regions for enhanced ductility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dual solder resist layer structure is disposed above patterned circuits in a bendable region, then the curvature of the bendable region is alleviated and physical stress on patterned circuits is reduced, but the thickness of the flexible circuit board increases which hinders bending
Solution Approach 1:
The patent applies local quality by providing a tin layer only in the bendable region above the patterned circuits, rather than uniformly across the entire board. This localized approach provides protection where needed while minimizing overall thickness increase that would hinder bending.
Solution Approach 2:
The patent changes the material parameter from solder resist to tin layer in the bendable region. Tin provides better protection against corrosion and physical damage while maintaining flexibility and bendability, resolving the contradiction between protection and bending capability.
2Length of moving object
If a thin tin layer is provided above patterned circuits in a bendable region, then bendability is maintained, but the tin layer may form apparent height differences with thick tin layer regions causing stress accumulation and cracking
Solution Approach 1:
The patent provides a thin tin layer specifically in the bendable region while maintaining thicker tin layers in non-bendable regions. This localized quality approach allows the thin tin layer to prevent stress accumulation in critical bending areas without creating harmful height differences that would lead to cracking.
Solution Approach 2:
The patent ensures that the thin tin layer in the bendable region is level with the thick tin layer in non-bendable regions, creating an equipotential surface that prevents stress accumulation at height differences and eliminates cracking risks.
3Length of moving object
If the thickness of copper in the bendable region is increased, then ductility and bendability are improved, but the overall complexity of the circuit board structure increases
Solution Approach 1:
The patent increases copper thickness only in the bendable region where it is needed for ductility and bendability, while maintaining standard thickness in non-bendable regions. This localized approach provides enhanced flexibility where required without unnecessarily increasing overall structural complexity.
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 design ensures the bendability and reliability of flexible circuit boards by reducing stress accumulation and preventing early damage from repeated bending, while maintaining proper processing compatibility.
Implementation Method 1
a thin tin layer is disposed above patterned circuits (that is, the conductive copper layer), thereby protecting the conductive copper layer below from corrosion, collision or scratching
Implementation Method 2
surfaces of a thin tin layer and a thick tin layer are level, that is, the two have the same height and have no substantial height difference, hence preventing the issue of stress accumulation
Implementation Method 3
a thickness of copper of the patterned circuits (that is, a conductive copper layer) in a bendable region is greater and a thickness of copper of the patterned circuits (that is, the conductive copper layer) outside the bendable region is smaller. Thus, better ductility is provided via the copper having a greater thickness in the bendable region
Data Source
AI summary
A flexible circuit board designed for chip integration is provided. The flexible circuit board includes an insulating substrate, a conductive copper layer, a first tin layer, a second tin layer, and a first solder resist layer. The first tin layer has a first tin thickness, and the second tin layer has a greater second tin thickness. A first tin surface of the first tin layer and a second tin surface of the second tin layer are substantially level.