Wiring Board Interface Roughness for Low Dielectric Loss
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Solution Overview
Problem
High-frequency communication equipment requires insulating materials with low relative permittivity and dielectric loss tangent to minimize transmission loss, but existing materials like polyimide and liquid crystal polymers do not adequately address interface roughness and adhesiveness issues in circuit boards.
Innovation Solution
A wiring board configuration with a first resin layer, wiring patterns on its surface, and a second resin layer between the patterns, where the interface roughness between the first and second resin layers is greater than between the first resin layer and the wiring patterns, using polymers like liquid crystal polymers, fluororesins, and aromatic polyether ketones, and incorporating alkali-soluble or acid-soluble particles to enhance adhesiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If liquid crystal polymer is used as insulating material to reduce dielectric loss, then transmission loss in high frequency band is reduced, but interface roughness and adhesiveness are insufficient
Solution Approach 1:
The patent applies local quality by creating different surface roughness characteristics at different interfaces. The first resin layer has a rough surface at the interface with the second resin layer (Rz1 ≥ 1.0 μm) to enhance adhesiveness, while maintaining a smooth surface at the interface with the wiring pattern (Rz2 < 1.0 μm) to reduce dielectric loss. This localized differentiation of surface properties resolves the contradiction between adhesiveness and transmission loss.
Solution Approach 2:
The patent changes the surface roughness parameter of the first resin layer by controlling the formation process to achieve different Rz values at different interfaces. By adjusting processing conditions such as heating temperature, pressure, and time during lamination, the surface roughness is optimized to be rough at the resin-resin interface and smooth at the resin-conductor interface, thereby simultaneously improving adhesiveness and reducing dielectric loss.
2Ease of manufacture
If polyimide is used as insulating material, then manufacturing is simple, but dielectric loss is high in high frequency band
Solution Approach 1:
The patent changes the material parameter from conventional polyimide to liquid crystal polymer, which has inherently lower dielectric loss in the high frequency band. This material substitution, combined with controlled surface roughness processing, achieves both low dielectric loss and maintainable manufacturing complexity.
3Reliability
If interface roughness is increased to improve adhesiveness, then adhesiveness is enhanced, but dielectric loss increases
Solution Approach 1:
The patent implements local quality by spatially differentiating surface roughness across the first resin layer. The surface at the interface with the second resin layer is made rough (Rz1 ≥ 1.0 μm) to maximize adhesiveness, while the surface at the wiring pattern interface is kept smooth (Rz2 < 1.0 μm) to minimize dielectric loss. This localized property differentiation allows each interface to be optimized for its specific function.
Solution Approach 2:
The patent segments the surface properties of the first resin layer into two distinct zones with different roughness characteristics. By controlling the lamination process parameters, the surface is segmented such that one interface develops roughness for adhesiveness while the other maintains smoothness for low dielectric loss, effectively separating these conflicting requirements into different spatial locations.
Data Source
AI summary
A wiring board including a first resin layer, wiring patterns arranged on at least one surface of the first resin layer, and a second resin layer disposed between the wiring patterns and on the wiring patterns, in which, in a cross section along a thickness direction, an interface roughness Rz1 of an interface between the first resin layer and the second resin layer is larger than an interface roughness Rz2 of an interface between the first resin layer and the wiring pattern; and applications thereof are provided.