Wiring Board Contact Layer for Fine Wiring
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Solution Overview
Problem
The challenge in manufacturing wiring boards with reinforcing material-containing insulating layers is the difficulty in forming fine wirings due to the rough surface resulting from desmear processing, which makes it hard to achieve high accuracy for wiring patterns with Line/Space (L/S) ratios of 15 μm/15 μm or less.
Innovation Solution
A wiring board structure is developed with a contact layer having a higher adhesion property than the insulating layer and a thickness smaller than the insulating layer, allowing for the formation of fine wiring patterns by exposing the wiring layer through openings in both layers, which are filled with via and wiring patterns, enabling accurate and precise wiring formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a reinforcing material-containing insulating layer is used to improve mechanical strength and reduce warping, then the mechanical strength is improved, but the surface roughness increases making fine wiring formation difficult
Solution Approach 1:
The insulating layer is segmented into two distinct layers: a lower insulating layer containing reinforcing material for mechanical strength, and an upper insulating layer without reinforcing material that provides a smooth surface for fine wiring formation. This segmentation allows each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
Different regions of the insulating structure are assigned different qualities: the lower layer has high mechanical strength due to reinforcing material, while the upper layer has smooth surface quality suitable for precise wiring patterns. Each layer's properties are optimized for its specific functional requirement.
2Object-generated harmful factors
If desmear processing is performed on the insulating layer to remove resin residues, then the surface is cleaned, but the surface roughness increases to about 800-1000 nm Ra value
Solution Approach 1:
Desmear processing is performed preliminarily on the lower insulating layer before forming the upper insulating layer. This preliminary action removes resin residues that would otherwise interfere with subsequent wiring formation, while the upper layer is then applied to restore surface smoothness.
Solution Approach 2:
The upper insulating layer acts as an intermediary layer between the processed lower insulating layer and the wiring patterns. It mediates the contradiction by providing a smooth surface that masks the roughness introduced by desmear processing, enabling precise wiring formation.
3Manufacturing precision
If the insulating layer thickness is reduced to enable fine wiring formation, then the wiring density increases, but the mechanical strength and warping resistance decrease
Solution Approach 1:
The solution moves from a single-layer insulating structure to a multi-layer insulating structure, adding a vertical dimension to the design. The lower layer maintains mechanical strength with reinforcing material, while the upper layer enables fine wiring with smooth surface, effectively resolving the contradiction through dimensional expansion.
Solution Approach 2:
The insulating structure uses composite materials strategy by combining two types of insulating layers: one with reinforcing material for strength, and one without reinforcing material for surface smoothness. This composite approach allows both mechanical strength and fine wiring formation to coexist.
Data Source
AI summary
A wiring board includes: a first wiring layer; a first insulating layer formed on the first wiring layer and including a reinforcing material therein, the first insulating layer having a first opening; a contact layer formed on the first insulating layer and having a second opening communicated with the first opening; and a second wiring layer comprising a second via and a second wiring pattern connected to the second via. The second wiring pattern is formed on the contact layer, and the second via is filled in the first and second openings. An adhesion property between the contact layer and the second wiring pattern is higher than that between the first insulating layer and the second wiring pattern, and a thickness of the contact layer is smaller than that of the first insulating layer.