Printed Wiring Board Via Structure for Uniform Seed Layer Deposition
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Solution Overview
Problem
Existing printed wiring boards face challenges in achieving smooth and uniform conductor layer connections due to uneven surfaces and inadequate thickness distribution in seed layers, leading to issues with adhesion strength, wiring width control, and connection reliability.
Innovation Solution
A printed wiring board design featuring a resin insulating layer with differently shaped inorganic particles forming a smooth inner wall surface and varying thicknesses in the seed layer portions, combined with a semi-additive manufacturing process to form a via conductor, ensures uniform seed layer deposition and stable connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a uniform thickness seed layer is formed on the inner wall surface of the opening, then the adhesion strength is improved, but the wiring width control and etching complexity worsen
Solution Approach 1:
The seed layer is designed with non-uniform thickness distribution: thicker at the bottom of the opening (for adhesion) and thinner at the top (for wiring width control). This local variation in thickness resolves the contradiction by optimizing different regions for different functions.
Solution Approach 2:
The inner wall surface of the opening is pre-treated to enhance adhesion before seed layer formation. This preliminary surface preparation ensures strong adhesion without requiring excessive seed layer thickness throughout, simplifying subsequent etching processes.
2Strength
If the seed layer thickness is increased to improve adhesion, then the adhesion strength is improved, but the wiring width control and stress concentration worsen
Solution Approach 1:
The seed layer thickness is optimized locally: thicker at the bottom for adhesion and thinner at the top for precise wiring width control. This prevents stress concentration while maintaining strong adhesion.
Solution Approach 2:
The seed layer thickness parameter is varied through the depth of the opening rather than maintained uniformly. This parameter change enables simultaneous achievement of strong adhesion and precise wiring width control without stress concentration.
3Manufacturing precision
If the inner wall surface is made smooth and uniform, then the seed layer deposition is improved, but the adhesion strength and connection reliability worsen
Solution Approach 1:
The inner wall surface is pre-treated with plasma or chemical etching to create microroughness that enhances adhesion. This preliminary action provides both good seed layer deposition and strong adhesion by increasing surface area and creating mechanical interlocking.
Solution Approach 2:
The inner wall surface structure is designed as a composite with different roughness characteristics at different scales: micro-roughness for adhesion and macro-smoothness for uniform deposition. This composite structure resolves the contradiction between adhesion strength and deposition uniformity.
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
The solution results in improved adhesion strength, controlled wiring width, reduced etching complexity, and enhanced connection reliability, with reduced stress concentration and increased productivity.
Implementation Method 1
a second conductor layer formed on a surface of 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 opening of the resin insulating layer and including the seed layer and the electrolytic plating layer formed on the seed layer
Data Source
AI summary
A printed wiring board includes a first conductor layer, a resin insulating layer having an opening, a second conductor layer including a seed layer and an electrolytic plating layer formed on the seed layer, and a via conductor including the seed and electrolytic plating layers and connecting the first and second conductor layers. The seed layer has a first portion on the surface of the insulating layer, a second portion on an inner wall surface in the opening of the insulating layer, and a third portion on a portion of the first conductor layer exposed by the opening of the insulating layer such that the first portion is thicker than the second and third portions, and the insulating layer includes resin and inorganic particles including first particles forming the inner wall surface and second particles embedded in the insulating layer and having shapes different from shapes of the first particles.