Wiring Board Recess Design for Void-Free Plating
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Solution Overview
Problem
In existing wiring boards with multilayer wiring structures, the connection reliability of via wiring lines and connection terminals is insufficient due to voids generated during the electrolytic plating process, which affects the electrical connection and stability.
Innovation Solution
The proposed wiring board design includes a recess portion on the surface of the wiring layer with a raised portion at its central bottom surface, facilitating improved embeddability of the conductor film and reducing void generation by promoting plating solution circulation and growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a recess portion is formed on the wiring layer surface before plating, then the embeddability of the conductor film is improved, but the manufacturing process complexity increases
Solution Approach 1:
The recess portion is formed in advance on the wiring layer surface before the plating process. This preliminary action allows the plating solution to better access and deposit metal on the wiring layer surface, improving embeddability without requiring complex real-time adjustments during plating.
Solution Approach 2:
The recess portion is formed only at specific locations where via holes are to be created, not across the entire wiring layer. This localized modification improves embeddability where needed while minimizing additional manufacturing complexity and material usage.
2Ease of manufacture
If the plating film is deposited from the seed layer on the inner wall surface of the opening portion, then the connection terminal is formed, but the opening portion is closed before the plating solution reaches the bottom surface of the recess portion, generating voids
Solution Approach 1:
The recess portion is formed in advance to create a geometry that facilitates plating solution flow. The recess allows the plating solution to reach the bottom surface of the wiring layer before the opening portion is completely closed by the deposited plating film, preventing void formation.
Solution Approach 2:
The recess portion introduces a vertical dimension to the plating process geometry. By creating a stepped structure with the recess, the plating solution can access the bottom surface through multiple paths (along the inner wall and through the recess), ensuring complete filling before closure.
3Ease of manufacture
If the bottom surface of the recess portion has a concave shape, then the etching process is simplified, but the distance from the deepest portion to the bottom of the opening portion becomes relatively long, delaying plating film growth
Solution Approach 1:
A raised portion is formed at the central portion of the recess bottom surface, creating a localized high point. This allows the plating solution to reach a critical point faster while still maintaining the overall recess geometry that facilitates manufacturing. The raised portion acts as an early nucleation site for plating film growth.
Solution Approach 2:
The raised portion is formed during the etching process as a preliminary structural feature. This pre-formed raised area provides a starting point for rapid plating film growth, compensating for the longer path length caused by the concave recess shape.
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 the connection reliability between the via wiring lines, connection terminals, and the wiring layer by minimizing voids and ensuring stable electrical connections.
Implementation Method 1
a seed layer is formed by electroless plating on a surface of the insulating layer or the solder resist layer including an inner wall surface of the opening portion
Implementation Method 2
electrolytic plating is performed on the seed layer, whereby the via wiring line and the connection terminal are formed
Data Source
AI summary
A wiring board includes: a wiring layer; an insulating layer laminated on the wiring layer; an opening portion penetrating through the insulating layer to the wiring layer; a recess portion formed in a surface of the wiring layer exposed from the opening portion of the insulating layer; and a conductor film formed in the opening portion of the insulating layer and the recess portion of the wiring layer, wherein the recess portion of the wiring layer includes a raised portion, which is raised higher than an outer peripheral portion of a bottom surface, at a central portion of the bottom surface.