Irregular Via Hole Design for Printed Wiring Board Plating
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Solution Overview
Problem
The challenge in forming dense wiring on printed wiring boards is that reducing the diameter of via holes leads to connection failures due to retained bubbles, which cannot be reliably injected with plating solutions, especially in blind via holes.
Innovation Solution
A printed wiring board design featuring a via hole with an irregular cross-sectional shape, including an expansion section that increases the cross-sectional area towards the first conductive layer, enhances the flow velocity of the plating solution, preventing bubble retention and ensuring reliable connection between conductive layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the diameter of the via hole is reduced to increase wiring density, then wiring density is improved, but bubbles are retained in the hole and plating solution cannot be injected, resulting in connection failure
Solution Approach 1:
The connection hole is designed with an asymmetric cross-sectional shape that is elongated in the thickness direction of the substrate layer. This asymmetric geometry allows the hole to be narrower in the lateral direction (increasing wiring density) while maintaining sufficient length for bubble removal during plating, thus resolving the contradiction between wiring density and connection reliability
Solution Approach 2:
The invention changes the geometric parameters of the connection hole by defining its cross-sectional shape as an irregular quadrangle with specific side length relationships. The hole is designed to be elongated in the thickness direction with controlled aspect ratios, transforming the conventional cylindrical hole geometry into a optimized shape that enables both high wiring density and reliable plating fill
2Area of stationary object
If a blind via hole is used to reduce footprint area, then footprint area is reduced, but bubbles are more likely to be retained and connection failure is more likely to occur
Solution Approach 1:
The blind via hole is designed with an asymmetric cross-sectional shape elongated in the thickness direction. This asymmetric geometry creates a tapered effect that facilitates bubble removal during plating while maintaining the blind via structure that reduces footprint area, thus resolving the contradiction between compact size and connection reliability
Solution Approach 2:
The connection hole has different cross-sectional dimensions at different locations: it is narrower at the substrate surface to save space but elongated in the thickness direction to enable proper plating fill. This local variation in geometry allows the hole to serve both functions of reducing footprint and ensuring reliable connection
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 effectively prevents bubble retention and ensures reliable connections between conductive layers, increasing wiring density and reducing defect occurrence rates in via holes.
Implementation Method 1
enhances the flow velocity of the plating solution, preventing bubble retention
Data Source
AI summary
A printed wiring board of the present invention includes an insulating substrate layer; a first conductive layer laminated to one surface of the substrate layer; a second conductive layer laminated to another surface of the substrate layer; and a via hole formed along an inner surface of a connection hole that is provided, in a thickness direction, through the substrate layer and the first conductive layer, the via hole electrically coupling the first conductive layer and the second conductive layer. A cross-sectional shape of the connection hole along at least one surface of the substrate layer is an irregular shape.