Printed Wiring Board Seed Layer Structure for Low-Loss Via Adhesion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing printed wiring boards face issues with insufficient adhesion between conductor circuits and resin insulating layers, leading to potential peeling and increased transmission loss, especially when subjected to impacts or high-frequency signals.
Innovation Solution
The printed wiring board incorporates a seed layer with a dual-layer structure comprising an alloy of copper, aluminum, and a specific metal, such as silicon, on the inner wall surface of the via conductor, which is formed with a smooth step-shaped cross-section to enhance adhesion and reduce peeling, while maintaining a smooth surface for low transmission loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional single-layer conductor structure is used, then the manufacturing process is simple, but the adhesion between conductor layers and resin insulating layer is insufficient leading to peeling
Solution Approach 1:
The seed layer is divided into two distinct layers: a first seed layer in direct contact with the resin insulating layer containing copper and a first metal (nickel, zinc, gallium, silicon, or magnesium) for strong adhesion, and a second seed layer on top containing copper and aluminum for conductivity and smooth surface formation. This segmentation allows each layer to perform its specific function optimally.
Solution Approach 2:
The patent employs composite material structures in multiple places: the first seed layer uses copper combined with specific metals (nickel, zinc, gallium, silicon, or magnesium) to achieve both adhesion and conductivity; the second seed layer uses copper-aluminum alloy for optimal electrical properties; the via conductor uses copper-nickel composite; and the resin insulating layer uses epoxy resin combined with inorganic particles. These composite structures resolve the contradiction by providing both strong adhesion and good conductivity.
2Loss of energy
If the inner wall surface of the via conductor is made smooth for low transmission loss, then transmission loss is reduced, but adhesion between the via conductor and resin insulating layer deteriorates
Solution Approach 1:
The patent applies different surface qualities to different locations: the first seed layer that contacts the resin insulating layer has a rougher surface texture that enhances mechanical interlocking and adhesion, while the second seed layer and via conductor surfaces are maintained smooth to minimize signal transmission loss. This local differentiation of surface quality resolves the contradiction between adhesion and transmission loss.
3Strength
If aluminum is added to the seed layer to improve adhesion, then adhesion strength increases, but the surface becomes less smooth increasing transmission loss
Solution Approach 1:
The patent segments the seed layer into two distinct layers with different compositions and surface characteristics. The first seed layer contains aluminum combined with copper and specific metals for strong adhesion to the resin insulating layer, while the second seed layer is a separate copper-aluminum alloy layer that forms a smooth surface for low transmission loss. This segmentation allows aluminum to provide adhesion without compromising surface smoothness.
4Reliability
If a multi-layer seed structure is implemented to improve adhesion, then peeling resistance increases, but manufacturing complexity and process difficulty increase
Solution Approach 1:
The patent specifies precise compositional parameters for each seed layer to achieve reliable adhesion while maintaining manufacturability. The first seed layer contains copper (5-50 at%), a first metal (nickel, zinc, gallium, silicon, or magnesium) at specific concentrations, and the second seed layer contains copper and aluminum in defined ratios. These parameter specifications enable consistent production with controlled adhesion properties without excessive manufacturing complexity.
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 enhances adhesion between conductor layers, reduces peeling, and minimizes transmission loss, ensuring reliable signal propagation and reducing noise, even under high-frequency conditions.
Implementation Method 1
a second conductor layer formed on the resin insulating layer and including a seed layer and an electrolytic plating layer formed on the seed layer, and a via conductor formed in the resin insulating layer such that the via conductor is connecting the first conductor layer and the second conductor layer and includes the seed layer and electrolytic plating layer extending from the second conductor layer
Data Source
AI summary
A printed wiring board includes a first conductor layer, a resin insulating layer formed on the first conductor layer, a second conductor layer formed on the resin insulating layer and including a seed layer and an electrolytic plating layer, and a via conductor connecting the first conductor layer and the second conductor layer and including the seed layer and electrolytic plating layer extending from the second conductor layer. The second conductor layer and via conductor are formed such that the seed layer includes a first layer including copper, aluminum and one or more metals selected from nickel, zinc, gallium, silicon and magnesium, and a second layer formed on the first layer and including copper. The seed layer in the via conductor has a first portion and a second portion such that the first portion is electrically connected to the second portion and has a portion formed on the second portion.