Flat Wiring Board Structure for High-Frequency Signal Integrity
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Solution Overview
Problem
Conventional wiring boards experience signal delay and delamination issues due to concavo-convex portions on the insulating and wiring layers, which are necessary for adhesion but detrimental to high-frequency signal transmission.
Innovation Solution
A wiring board design featuring reinforcing pads and vias that increase adhesion between insulating and wiring layers without concavo-convex portions, using a semi-additive method to form reinforcing pads and vias within openings in the plain layers, allowing gas escape during thermal curing and preventing delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If concavo-convex portions are formed on the insulating layer and wiring layer surfaces, then adhesion between layers is improved, but signal transmission delay increases
Solution Approach 1:
A roughening layer is introduced as an intermediary between the insulating layer and wiring layer. This separate layer provides the necessary surface roughness for adhesion without requiring modification of the wiring layer surface, thus maintaining signal transmission performance while achieving layer bonding.
Solution Approach 2:
The adhesion function is separated from the wiring layer structure. Instead of making the wiring layer surface concavo-convex, the roughening function is assigned to a dedicated roughening layer, allowing the wiring layer to remain flat for optimal signal transmission.
2Loss of time
If the wiring layer surface is made flat to reduce signal delay, then signal transmission efficiency is improved, but adhesion between layers deteriorates causing delamination
Solution Approach 1:
The roughening layer serves as a mediator that provides mechanical interlocking between the flat wiring layer and the insulating layer. The wiring layer surface remains flat for signal transmission, while the roughening layer creates anchor points for adhesion.
Solution Approach 2:
Surface roughness is localized to the roughening layer rather than being applied to the entire wiring layer surface. This allows the wiring layer to maintain its flat geometry for signal transmission while the roughening layer provides localized adhesion points.
3Strength
If conventional roughening processes are used to increase adhesion, then layer bonding is improved, but delamination occurs during thermal curing due to gas entrapment
Solution Approach 1:
The roughening layer is formed with a porous structure containing numerous fine holes. These pores allow gas to escape during thermal curing, preventing gas entrapment and subsequent delamination while maintaining surface roughness for adhesion.
Solution Approach 2:
Gas escape paths are extracted and provided through the fine holes in the roughening layer. This removes the harmful effect of gas entrapment during thermal curing while preserving the adhesion benefits of surface roughness.
Data Source
AI summary
A wiring board includes a first wiring layer, an insulating layer that is arranged on the first wiring layer, and a second wiring layer that is arranged on the insulating layer. The first wiring layer includes a first plain layer, an opening that penetrates through the first plain layer, and a reinforcing pad that is arranged in the opening. The second wiring layer includes a second plain layer. The insulating layer includes a reinforcing via that connects the reinforcing pad and the second plain layer.