Wiring Board Via Pad Gap Design for Adhesion and Precision
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Solution Overview
Problem
The miniaturization of wiring layers on insulating layers is hindered by the roughness of the insulating surface, leading to potential residues and electric short circuits due to the anchor effect, making it difficult to form fine wiring layers with narrow pitches.
Innovation Solution
A wiring board design that includes a gap between the via and the insulating layer in the through hole, where the via is coated with a pad larger than the hole, and the wiring layer fills this gap, improving adhesion and preventing groove formation, thus enhancing the reliability of connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the surface of the insulating layer is roughened to improve adhesion, then the wiring layer adheres tightly onto the insulating layer by the anchor effect, but it becomes difficult to form a fine wiring layer on the insulating layer due to residues and electric short circuits
Solution Approach 1:
The insulating layer surface is segmented into two distinct regions: a roughened region (first region) that provides anchor effect for adhesion, and a smooth region (second region) that enables precise wiring layer formation. This segmentation allows each region to fulfill its specific function without interfering with the other, resolving the contradiction between adhesion strength and wiring precision.
Solution Approach 2:
Different regions of the insulating layer are given different surface qualities: the first region has roughness to enhance adhesion, while the second region has smoothness to facilitate precise wiring layer formation. This local differentiation of surface properties allows the system to simultaneously achieve both strong adhesion and high manufacturing precision.
2Length of moving object
If the wiring layer pitch is narrowed to achieve miniaturization, then the wiring layer can be made finer, but residues occur due to the ruggedness of the roughened insulating layer surface
Solution Approach 1:
The insulating layer is divided into a roughened first region and a smooth second region. The smooth second region provides a residue-free surface that enables precise formation of fine wiring layers with narrow pitches, while the roughened first region maintains its anchor effect for adhesion. This segmentation eliminates the residue problem that would otherwise occur on uniformly roughened surfaces.
Solution Approach 2:
The smooth region is specifically positioned where the wiring layer will be formed, providing a locally optimized surface quality that prevents residue formation during miniaturization processes. This local smoothness contrasts with the surrounding roughened area, creating an ideal environment for precise wiring layer formation.
3Ease of manufacture
If desmearing is performed to remove resin smear in the through hole, then the through hole can be formed, but the surface of the insulating layer is etched and roughened
Solution Approach 1:
The insulating layer surface is segmented into a roughened first region and a smooth second region. The roughened first region results from the necessary desmearing process for through hole formation, while the smooth second region is created by a subsequent polishing or planarization process. This segmentation allows the system to accept the surface roughness from manufacturing necessity while compensating with a controlled smooth region.
Solution Approach 2:
The harmful effect of surface roughening from desmearing is converted into a beneficial feature by strategically positioning the roughened region to provide anchor effect for adhesion. The roughness that would otherwise be detrimental is transformed into a useful property for bonding the wiring layer to the insulating layer.
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 design allows for the successful miniaturization of wiring layers by reducing residue formation and improving adhesion, ensuring reliable connections and preventing disconnections, even with increasingly smaller pitches.
Implementation Method 1
A pad 71P filling a gap S1 is formed on an end surface 64A of the via 64
Implementation Method 2
A wiring layer adheres tightly onto the insulating layer by the anchor effect of the roughened insulating layer
Data Source
AI summary
A wiring board includes a first insulating layer coating a first wiring layer. A first through hole is opened in a surface of the first insulating layer and exposes a surface of the first wiring layer. A first via arranged in the first through hole includes an end surface exposed to the surface of the first insulating layer. A gap is formed between the first insulating layer and the first via in the first through hole. A second wiring layer is stacked on the surface of the first insulating layer and the end surface of the first via. The second wiring layer includes a pad filling the gap. The pad is greater in planar shape than the first through hole.