Flex-Rigid PCB Variable Copper Thickness for Bending Durability
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Solution Overview
Problem
Flex-rigid printed wiring boards face challenges in maintaining flexibility and durability of the flexible portion while ensuring conductivity in the rigid portion, as forming copper layers with different orientations increases wiring resistance and reduces flexibility.
Innovation Solution
The solution involves forming a conductor layer on a base film with a thinner average thickness in the flexible region compared to the rigid region, using a sputtering method or etching to achieve a thickness ratio where the flexible portion is less than one-third of the rigid portion, and incorporating a high elastic modulus rigid layer, such as a glass fiber-containing layer, to alleviate stress and maintain conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper layers with different orientations are formed to suppress disconnections and increase durability, then durability of the flexible portion is improved, but the thickness of the flexible portion increases causing loss of flexibility
Solution Approach 1:
The patent applies local quality by forming copper layers with different thicknesses in different regions: the flexible portion has a thinner copper layer (first thickness) while the rigid portion has a thicker copper layer (second thickness). This allows the flexible portion to maintain flexibility while the rigid portion ensures durability and connection stability.
Solution Approach 2:
The patent changes the parameter of copper layer thickness across different regions. By controlling the copper layer thickness to be smaller in the flexible portion and larger in the rigid portion, the patent optimizes both flexibility and durability without requiring multiple copper layers with different orientations.
2Ease of operation
If copper layers are thinned by etching to retain flexibility, then flexibility of the flexible portion is improved, but the thickness of copper layers in rigid parts is reduced leading to increased wiring resistance
Solution Approach 1:
The patent implements local quality by differentiating copper layer thickness based on functional requirements: thin copper layers in the flexible portion minimize bending stress and maintain flexibility, while thick copper layers in the rigid portion ensure low wiring resistance and high conductivity for component mounting.
Solution Approach 2:
The patent segments the copper layer thickness into two distinct values: a first thickness for the flexible portion and a second thickness for the rigid portion. This segmentation allows each region to have optimal conductivity and flexibility properties without compromising the other.
3Reliability
If multiple copper layers are formed to increase durability, then durability against folding is improved, but the thickness of the flexible portion increases resulting in loss of flexibility
Solution Approach 1:
Instead of forming multiple copper layers with different orientations, the patent changes the parameter of copper layer thickness. By using a single copper layer with variable thickness (thinner in flexible portion, thicker in rigid portion), the patent achieves durability without compromising flexibility.
Solution Approach 2:
The patent applies local quality by making the copper layer thickness location-dependent. The flexible portion has a thinner copper layer to maintain flexibility, while the rigid portion has a thicker copper layer to provide durability against folding and mechanical stress.
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 approach enhances durability and flexibility of the flexible portion while minimizing wiring resistance and ensuring long-term reliability by distributing stress evenly across the flexible portion, preventing breakage and maintaining conductivity.
Implementation Method 1
During thinning, for example, when using sputtering method to form a thin conductor layer, the minimum thickness permitted by the step is preferable
Implementation Method 2
this reduces the stress generated in the conductive internal portion along the bend, thereby retaining the flexibility of the flexible portion while increasing its fracture-strength. However, half-etching of the copper layers also reduces the thickness of the copper layers formed in the rigid parts
Data Source
AI summary
A flex-rigid printed wiring board is provided which can retain flexibility of a flexible portion while increasing durability of the flexible portion against folding, and can ensure conduction in a rigid portion, and a method of manufacturing the printed wiring board. The flex-rigid printed wiring board includes a conductor layer provided on at least one face of a base film, one region of the wiring board containing the base film being a rigid region, an another region containing the base film being a flexible region. The average thickness “tf” of the conductor layer on the base film formed in the flexible region and the average thickness “tR” of the conductor layer on the base film formed in the rigid region satisfy the relationship of tf<tR.